The invention relates to a method of and a device for automatically adjusting the ignition timing of a controlled ignition engine in relation to the selected operating conditions for the engine. The conditions include, but are not limited exclusively to the operation of the engine with an optimum spark advance for obtaining a maximum power output therefrom.
It has been proposed in the prior art to measure various different specific parameters for determining the operating condition of the engine. More specifically, parameters such as the running speed, i.e., RPM, temperature, vacuum in the intake manifold, etc. characterize the operating condition of the engine, and are used in appropriately adapted methods, e.g., by mathematical computations, to determine the spark advance corresponding to the desired operating condition of the engine, and for causing sparking at a time corresponding to the desired spark advance.
According to U.S. Pat. No. 3,875,912 the spark timing is adjusted so that the "explosion" in the cylinder head occurs at a predetermined angular position of the crankshaft for at least one cylinder. To accomplish this the pressure in the specified cylinder is measured by means of a pressure sensor which provides an electronic pulse having a sharp leading edge. The time at which the pressure reaches, as the signal increases, a preselected threshold value is defined as the "explosion" time.
According to British Patent No. 1,483,611 two different stages of the combustion of the fuel mixture in the cylinder are sensed. The first stage is after the initiation of the spark and corresponds to a low pressure stage. The second stage occurs at a subsequent point in time when a sudden rise in both the pressure and temperature within the cylinder is observed. The British Patent teaches that the commencement of the second stage can be sensed and the spark advance is adjusted so that said commencement of the second stage occurs at one fixed preselected crankshaft angular position, without regard to the other variables which influence the spark timing requirement.
German Patent No. 1,476,322 teaches the control of the spark timing in relation to a measurement of the engine output, as indicated by two pressure valves, and measured by pressure sensors located in the engine cylinders.
According to the published German patent application No. 2,030,679, variations in the engine torque can be detected and the spark timing adjusted in response to the detected value of the engine torque.
The prior solutions may give satisfactory results but do not permit accurate adjustment of the spark timing to the optimum value for maximum engine output.
In another prior art method, described in French patent application No. 2,404,121, a pressure sensor is used to detect the pressure peak in at least one cylinder of the engine in relation to the angular position of the crankshaft. The spark timing is adjusted so that this pressure peak occurs at a preselected angular position of the crankshaft. The disadvantages with this solution result from the high cost of present day pressure sensors capable of being used in this capacity, and from the requirement of having to substantially change the design of some of the parts of the engine in order to allow positioning of the pressure sensors.